The invention relates to an improved process for manufacturing dairy products.
It is known that the manufacture of dairy products--this expression comprising yogurts, fresh cheeses, renneted cheeses and "large curds"--comprises the formation of what is called the curd which is itself, at least in part, the result of the acidifying action on the starting material--namely the milk--of one or several acids and/or of one or several bacterial microorganisms of the family of acidifying lactic ferments, possibly in the presence of a coagulating enzyme and/or of one or several lactic ferments with flavoring action.
It is also known that microorganisms of the family of lactic ferments, just as other bacteria, when they are in the presence of specific bacteriophages, are attacked and lysed, that is to say destroyed, by these viruses which grow at their expense.
Now, the growth of the bacteriophages and the subsequent destruction of the lactic ferments is manifested, according to the nature of the lactic ferments concerned, by a disturbance of the acidification--and, consequently, of the formation of the curd, of which disturbance the economic consequences may be disastrous--and/or by disturbance of the organoleptic qualities of the dairy products obtained.
It follows that counteracting the proliferation of bacteriophages or more simply of phages, which withstand conventional pasteurisation treatments, constitutes one of the major preoccupations of the dairy products industry.
Thus, it has been proposed to resort to disinfectants such as hypochlorites, iodophores and formol; but even with strict hygiene (particularly by sterilization of the air and of the equipment from the pail to the manufacturing tank), it is difficult and expensive to remove the bacteriophages completely.
It has also been proposed to resort to take advantage of the fact that the phages need the presence of calcium ions to be able to infect bacteria. Thus, so-called "anti-phage" culture media, adapted to remove or block calcium ions, have recently appeared on the market; they are, generally, complex mixtures containing milk dehydrated or not, growth factors and large amounts of phosphates to sequester the calcium ions.
Now, these large amounts of phosphates present in the anti-phage media can cause metabolic damage to lactic yeast cultures.
And, especially, the complexing of the calcium has a negative influence on the cheese making suitability, in particular on coagulation (lengthing of the coagulation time, less firmness of the gel).
It has again been proposed either to eliminate the so-called maturation phase of the milks for cheese making, or to change lactic ferments each time the tank is refilled.
It is true that, in the first case, the lactic ferments being directly seeded into the manufacturing tank during the refilling of the latter, the phages present are trapped in the curd network formed during the clotting after the addition of the rennet which comes into action preferably as soon as possible after the seeding; however, besides the high cost of this method of working, the suppression of ripening is not without consequences and remains therefore necessary in the case of milks treated thermally by cold storage or a pasteurisation treatment.
In the second case, the risk of attack of the phages and the consequences of the latter are considerably reduced but, on the other hand, the production costs are considerably increased; in addition, the rotation of the strains, that is to say the change of the strain of lactic ferments on each replenishment, results in variations in the matter of acidification times, in the matter of the amount of ferments to be added and especially in the matter of the organoleptic qualities of the finished dairy products.